The invention relates to a shock-absorbed vehicle steering wheel.
Steering wheels are normally composed of a hub with a steering wheel mounting and of a handling region for the driver, in particular a steering wheel rim. To increase the comfort and the driving safety, it is advantageous if vehicle vibrations, which arise through various causes and which are transferred to the steering wheel, in particular to the steering wheel rim, can be damped or entirely suppressed. For this purpose, for example so-called vibration neutralizers are used. A known vibration neutralizer contains a mass, mounted elastically in the steering wheel, which is set into vibration at the inherent frequency of the vibration neutralizer and thus takes up the vibration energy of the steering wheel. With these systems, it is disadvantageous on the one hand that they can be adapted only to individual frequencies and on the other hand that they take up a large amount of space inside the steering wheel or the hub.
It is an object of the invention to provide a shock-absorbed steering wheel including a damping means that is tunable in a defined frequency range and requires a relatively small amount of space for the shock-absorbing components.
This is achieved in a steering wheel which comprises a hub with a steering wheel mounting and a handling region for a driver. The handling region is, in particular, a steering wheel rim. A vibration damper is provided in a path of the flux of force between the steering wheel mounting and the handling region. The vibration damper has damping characteristics which are adjustable via one of an electrical and magnetic field. The vibration damper is arranged, as it were, between the hub and the steering wheel rim, so that the steering wheel mounting and the steering wheel rim can be neutralized with regard to vibration. By means of the strength of the electrical or magnetic field, for example via an applied voltage or an electric current, the damping characteristics, i.e. the vibration frequencies which are able to be damped, can be adjusted in a simple manner. An additional neutralizer mass can be dispensed with.
Preferably, the vibration damper has a substance intercalated into the flux of force, the hardness and/or viscosity of such substance being variably adjustable by the electrical or magnetic field. Hardness and viscosity have influence on the mechanical vibration characteristics of the substance and, hence, the vibration frequencies which are able to be damped.
The substance is preferably an electrorheological fluid. A commercially available electrorheological fluid can be used, which is distinguished in that its viscosity can be altered in a wide range by the influence of an electrical field. With high field intensities, these fluids behave, up to certain limiting conditions, like a ,,softxe2x80x9d solid body designated here as ,,semi-solid body modexe2x80x9d, which permits a transfer of force via the electrorheological fluid, but at the same time is able to be altered through the strength of the field intensity in its hardness and hence in its vibration characteristics.
It is also conceivable to use as a substance a magnetorheological fluid, the viscosity of which is able to be influenced by a magnetic field. Of course, owing to the limited amount of space available, the use of an electrorheological fluid presents itself, because electrodes for the generation of an electrical field, such as for example wires or metal plates, can be arranged more simply in the steering wheel than coils for the generation of a magnetic field.
In order to achieve a frequency-dependent vibration damping, preferably a control unit is provided, which can determine the intensity of the electrical or magnetic field generated by the electrodes, by adjusting the voltage applied thereto and the flow of current, respectively. The control unit is preferably connected with sensors which can detect vibrations of the steering wheel, in particular of the steering column, the control unit being able to adjust the field intensity as a function of the frequency of the detected vibrations, in order to thus reduce the vibration amplitude of the steering wheel. In particular, the control unit can preferably vary the field intensity such that no vibrations are stimulated in the handling region.
In a preferred embodiment of the invention, the hub or the handling region has at least one projection which projects into a depression formed on the respective other part, the substance being provided between the projection and the depression. The projection on the handling region can be provided for example in the region of a spoke. The hub and the steering wheel mounting, respectively, and the handling region are coupled with each other by the substance. The substance is preferably operated in ,,semi-solid body modexe2x80x9d, because thus on actuation of the steering wheel a compression stress can be transferred through the substance, in order to carry out a steering movement. Nevertheless, the hardness and hence the damping characteristics can still be adapted via the strength of the field intensity. This system can also be provided in the region of the hub, where there is more space to accommodate the vibration damper, the hub being divided into several parts and the substance connecting the hub parts with each other.
The hub and the handling region or the hub parts are preferably only separated from each other by a narrow intermediate space (0.1 to 5 mm wide), which is filled with the electrorheological or magnetorheological fluid. As the hub and the handling region do not touch each other directly at any point, vehicle vibrations transferred for example via the steering shaft to the steering wheel mounting are not transferred by means of direct contact of the hub to the handling region or of the hub parts, but rather can only arrive at the steering wheel rim via the electrorheological or magnetorheological fluid. However, the hardness or viscosity of the substance can be adapted so quickly and flexibly to the respective vibration frequencies via the strength of the field intensity, that vibrations of the handling region can be effectively damped.
In another preferred embodiment of the invention, the vibration damper comprises a space which is filled with the substance and forms a closed ring. Here, too, this space is constructed such that it separates the hub and the handling region from each other, and such that the hub and the handling region are coupled with each other via this space.
It is advantageous if the space has a shape which deviates from a circular ring, for example has the form of a polygon. In this way, the geometry of the ring-shaped space can be utilized in order to make possible the transfer of force via the substance. The substance forms a ,,semi-solid bodyxe2x80x9d in the form of a polygonal ring, which is prevented by its shape from rotating in the ring-shaped space, if a rotational force is exerted onto it. Instead of this, the rotational force originating from the steering wheel mounting (and the hub, respectively) or the handling region is transferred without play onto the other respective steering wheel section. The corners of the polygon act as projections which project into depressions of the other part, in order to achieve on actuation of the steering wheel a compressive stress through the substance provided between the projections and the depressions.
In order to increase the transfer of force between the parts which are coupled by the substance, the walls delimiting the space preferably have a structure which is designed such that it supports adhesion of the substance to the walls. Hereby, the steering becomes more direct, because a slippage between the substance and the wall is largely eliminated, when the substance is operated in the ,,semi-solid body modexe2x80x9d.
In order to ensure a reliable steering actuation even in an extreme operation, for example in the case of an extremely vigorous and rapid steering movement or in the case of failure of the electrical or magnetic field, the vibration damper is advantageously designed such that in extreme operation a continuous form-fitting connection is made possible between the handling region and the steering wheel mounting. In this case, the vibration damper can be bypassed, so that a direct coupling exists between the parts adjoining the substance.